Typically, gravity feed blood filtration devices require user manipulation of vent filters during the filtration process. The manipulation of the vent filters must occur at the proper time during the filtration process or the system will not filter properly and blood being filtered may be rendered unusable. Since user manipulation of vent filters is time consuming and costly, it is desirable to achieve a liquid filtration device which may filter blood without the manipulation of vent filters or filtration devices. Moreover, blood filtration devices usually allow liquid to remain within the filtration device after filtration has occurred. This remaining liquid, referred to as a hold up volume, is often greater than the desired maximum amount. Also, blood filtration devices allow an undesirably high amount of air that is purged therefrom to be left in the receiving blood bag.
The filtration device disclosed in U.S. Pat. No. 5,472,605, and entitled "A Filtration Device Usable for Removal of Leukocytes and Other Blood Components" issued Dec. 5, 1995, and the filtration device disclosed in U.S. Ser. No. 08/524,049, U.S. Pat. No. 5,798,041, and entitled "an In-Line Liquid Filtration Device Usable for Blood, Blood Products and the Like" filed Sep. 6, 1995, and the filtration device disclosed in U.S. Ser. No. 08/449,362, abandoned, and entitled "A Filtration Device Usable for Removal of Leukocytes and Other Blood Components" filed May 24, 1995, and the filtration device disclosed in U.S. Ser. No. 08/661,804, abandoned, and entitled "A Filtration Device Usable for Removal of Leukocytes and Other Blood Components" filed Jun. 11, 1996, which are hereby incorporated by reference and made a part of the disclosure herein, overcome the aforementioned vent filter manipulation problem. However it is desirable to further reduce the hold up volume of this device, and to allow the device to be used in a vertical orientation, and not drain the outlet tubing so that the blood left in the outlet tubing can be used for cross matching, and to further reduce the manufacturing cost thereof, while maintaining an acceptable total filtration time.
Furthermore, it is desirable to eliminate air pockets within the device. Air pockets will reduce the effective filtration system area by reducing the area of the filter elements where blood may flow.
Although blood filtration devices may provide a means to separate gas from liquid and then vent the gas from the device to atmosphere, they are usually not designed to automatically drain the liquid from the upstream side of the device once filtration has stopped. Moreover, blood filtration devices typically do not have features which prevent the tubing attached thereto from becoming kinked thus impeding blood flow. It is, therefore, desirable to achieve a liquid filtration device which filters blood without the manipulation of vent filters, minimizes hold up volume, that automatically drains the upstream side of the device when the filtration process is complete, that minimizes the volume of air that is added to the receiving blood bag, that reduces air pocket therein, that reduces the possibility of kinked tubing when the device is assembled into a filtration system and packaged for shipping, that can be used in a vertical orientation, and that does not drain the outlet tubing.